A number of processes and apparatus have been developed to carry out an "open-end" spinning process or a "round-about" spinning process. For example, as discussed on pages 322-327 of the book "Textile Yarns Technology, Structure, & Applications" by B. C. Goswami et al, John Wiley & Sons, New York (1977), the open-end spinning process may also be referred to by the term "break spinning" since a roving is broken at one point into individual fibers and the fibers transferred to another point for reassembly into a thread or yarn. In a round-about spinning, a continuous core thread or filament is fed along the line of thread formation with the individual fibers being reassembled therearound as a sheath or outer layer.
A typical method of open-end spinning is disclosed in Malliand Textilberichte 1975, Vol. 9, pages 690 ff., where a card sliver or roving of staple fibers is first separated into the individual fibers by means of a rapidly rotating roller, the fibers then being transferred to a rotating cylindrical sieve drum. Rotation of this drum introduces a moment of torsion into the collected fiber mass so that the individual fibers are assembled into a more or less compact bundle along a line of filament or thread formation on the drum with a real twist imparted to form the thread or yarn. This process presents certain disadvantages because the thread being formed tends to be very unstable in its position on the drum, resulting in uneven thread diameters and frequent thread breakage.
Another known process of this type is disclosed in the German Offenlegungsschrift No. 24 49 583 wherein the individual fibers are twisted into a thread or yarn in the nip between two rollers or sieve drums which rotate in the same direction around parallel axes. The individual fibers are fed perpendicularly to the direction in which the formed thread is drawn off from the nip. Inside of each of the drums is an air suction device, the open end of which is directed toward the nip in which the thread is formed. Air currents produced by the suction devices press the fibers against the drum walls in the region of the nip. This particular method is disadvantageous in that the air currents produced by suction oppose the desired direction of twisting the thread. Again, it is most difficult to achieve stable thread forming conditions except by using extraordinary measures.
According to the specifications of the German Offenlegungsschriften No. 26 56 787 and No. 27 39 410, the individual fibers are introduced by an air stream through a feed channel into the thread forming zone extending in the narrowest gap between rollers. Here, the feed channel is inclined toward the thread forming zone in such a way that the air stream has a vector of movement in the draw-off direction of the thread. German Offenlegungschriften No. 27 39 410 corresponds to U.S. application Ser. No. 937,798, filed Aug. 29, 1978, now U.S. Pat. No. 4,165,600.
An especially useful open-end or round-about spinning process with suitable apparatus is disclosed in our earlier U.S. application with coinventors Dammann and Schippers, Ser. No. 782,310, now U.S. Pat. No. 4,130,983. In this case, various feed arrangements are used to convey the individual fibers into the thread forming zone, i.e. into the narrowest gap formed between oppositely moving air-permeable surfaces of paired sieve belts, drums or rollers, said gap lying between parallel belts or in a plane substantially normal to the curved surfaces of the drums or rollers. The individual fibers may be fed perpendicularly to the line of rotating thread formation in said gap but are generally introduced into the gap by an air stream with a substantial component or vector of movement in the same direction as the thread draw-off.
When spinning fibers of a certain origin in the earlier described processes, a problem has existed in that a relatively large proportion of the spinning fibers tend not to be twisted into the thread or to be only incompletely twisted into the thread, thereby causing an impairment of the strength, workability, handle and appearance of the thread or yarn product. This problem is only partially avoidable by means of a very sensitive machine adjustment, the processing variables being difficult to control and never precisely reproducible.